Exhothermic composition for hot tops

ABSTRACT

IN AN EXOTHERMIC COMPOSITION FOR A HOT TOP ON A FOUNDRY MOLD, THERE ARE PROVIDED FROM ABOUT 5 TO 30% BY WEIGHT OF FIBERS EACH HAVING A LENGTH OF ABOUT 0.5 TO 30 MM., THE FIBERS BEING EVENLY DISPERSED IN THE EXOTHERMIC COMPOSITION TO SEIZE THE FINE PARTICLES OF THE COMPOSITION AND TO PERMIT THE ESCAPE OF COMBUSTION GAS BUBBLES THROUGH NUMBEROUS CAVITIES FORMED THEREIN.

United States Patent Office 3,759,724 Patented Sept. 18, 1973 3,759,724EXOTHERMIC COMPOSITION FOR HOT TOPS Sunao Nishi, Nagasaki, Shojirolkeda, Tokyo, and Takayoshi Torii, Ichikawa, Japan, assignors to ShintoKogyo Kabushiki Kaisha, Nagasaki-shi, Nagasaki-ken, Japan No Drawing.Filed Sept. 14, 1971, Ser. No. 180,468 Int. Cl. B28b 7/36 US. Cl.106--38.22 4 Claims ABSTRACT OF THE DISCLOSURE In an exothermiccomposition for a hot top on a foundry mold, there are provided fromabout 5 to 30% by weight of fibers each having a length of about 0.5 to30 mm., the fibers being evenly dispersed in the exothermic compositionto seize the fine particles of the composition and to permit the escapeof combustion gas bubbles through numerous cavities formed therein.

BACKGROUND OF THE INVENTION This invention relates generally to chemicalcompositions and is more specifically directed to an improved exothermiccomposition for particular use in retaining heat on the surface of a hottop supplying molten metal to a solidifying casting in a foundry mold inorder to compensate for its shrinkage.

Conventional counterparts of such an exothermic composition are mostlymixtures of powdered flammable metal such as aluminum andcalcium-silicon alloy, oxidizer, oxidation accelerator, and extender.Being in the form of finely divided particles, the prior artcompositions when charged onto the surface of a hot top on a foundrymold in operation are partly blown upward, dustlike, into the air due tothe convectional currents produced by the high temperature hot top andto the gases evolving therefrom as a result of the exothermic reaction.The dustlike suspension of the fine particles in air not only lowers thevisibility of foundry atmosphere and so hampers the molding operationbut is highly undersirable for the hygiene for foundrymen.

SUMMARY OF THE INVENTION Therefore, it is an object of the presentinvention to provide an improved exothermic composition for particularuse in retaining the heat of a hot top on a foundry mold.

Another object of the invention is to provide an exothermic compositionsuch that substantially no fine particles included therein are releasedtherefrom when the composition is charged onto the surface of a hot topat an elevated temperature.

Another object of the invention is to provide an exothermic compositionfor a hot top having an improved heat-retaining property.

A further object of the invention is to provide an exothermiccomposition wherein fibers of substantially any substance, be theyorganic or inorganic, are employable to obtain the desired results ifthey are within the specified dimensions.

According to this invention, briefly summarized, there is provided apowdered exothermic composition including a powdered flammable metal,oxidizer, oxidation accelerator and an extender for a hot top on afoundry mold which contains, in addition to its known ingredients, fromabout 5 to 30% by weight of fibers each having a length of about 0.5 to30 mm.

The above stated and various other objects, advantages and features ofthe present invention will become more apparent and understandable fromthe following detailed description of the invention together with somespecific example thereof.

DETAILED DESCRIPTION OF THE INVENTION The powdered flammable metal,oxidizer, oxidation accelerator and extender to be included in theexothermic composition in accordance with the present invention may besuitably selected from such conventionally known and widely usedsubstances as powdered aluminum, powdered calcium-silicon alloy, ironoxide, manganese dioxide, sodium nitrate, quartz sand and dolomite. Theingredients so selected may be also suitably compounded in accordancewith the prior art.

The fibers to be added to the composition according to the novelteachings of this invention may be either of an inorganic substanceincluding such naturally available mineral fibers as asbestos, forexample, an amosite and such man-made mineral fibers as glass wool andslag wool, or of an organic substance including such natural fibers asvegetable and animal fibers, regenerated fibers, and synthetic fibers.Additional examples of materials employable for the same objects of theinvention include wood and paper scraps, bagasse, brans and numerousother readily obtainable materials irrespective of whether they areoriginally in the form of fibers or not, the materials originally not inthe form of fibers being suitably processed into the desired fibrousdimensions hereinafter set forth. In fact, the fibers of practically anysubstance are adaptable to the exothermic composition provided that theyprevent the fine particles of the composition from being blown away uponcontact with a hot top at an elevated temperature and at the same timeretain the heat of the hot top.

The temperature at the surface of a hot top on a foundry mold inoperation usually ranges between about 1,300 and l,600 C. so thatextremely powerful convection currents are produced thereupon.Heretofore, upon contact with the hot top, the exothermic compositionhas inevitably had part of its fine particles swept upward by suchconvection currents. The composition so charged onto the surface of thehot top must be further leveled or flattened into uniformly thick layer,in which case the combustion gases captured temporarily in thecomposition as a result of the exothermic reaction are instantly blastedup, thereby causing compartively lightweight and finely dividedparticles of the composition to be swept up and hence to be suspended inthe air.

Because of the addition of the aforementioned fibers to the exothermiccomposition in accordance with the present invention, such fineparticles are seized by the thickly interlaced fibers in such a mannerthat they are not scattered about by any such external forces as theconvectional currents or the blasting up of the once-captured combustiongases. Moreover, in the case of fibers of an inorganic substance, thegases produced by the combustion of the exothermic composition are nottrapped therein as mentioned above but are made to escape therefromthrough numerous cavities formed by the interlaced fibers. Hence thereis no possibility of the fine particles being blown upward during theleveling operation.

If, on the other hand, such organic fibers as those listed above areadded to the composition, the fibers are naturally burnt into ashthereby to form numerous cavities again in the process of combustion.The resultant porosity of the layer permits ready escape of thecombustion gases so that the particles are not blown upward during theleveling operation as in the precedingly considered case of theinorganic fibers. It is also noteworthy that the cavities produced bythose fibers in the composition contribute toward formation of anextremely lightweight, porous and soft residual layer on the hot topupon completion of the combustion, the better to retain the heat of thehot top.

At least theoretically, the longer and the greater in amount the fibersare, the better are the fine particles of the composition prevented frombeing scattered about. Practically, however, excessively long fibers arelikely to prevent uniform intermingling of the composition ingredientsincluding themselves. And when added in an overly large amount, thefibers may melt and solidify after being once reduced to ash and thusdeteriorate that heat retaining property of the composition.

We have experimentally verified that for the best results, the fibersshould each have a length of about 0.5 to 30 mm. and should be added tothe desired composition in an amount ranging from about 5 to 30% byweight. Fibers less than about 0.5 mm. in length lead to poor seizure ofthe fine particles, and those more than Sample I II III IV Powderedaluminum 15 15 15 15 Aluminum ash 70 6O 50 40 Fluorspar 5 5 6 5 Sodiumnitrate. 3 3 3 3 Iron oxide 7 7 7 7 Asbestos 0 10 20 30 Bulk specificgravity 0. 97 0. 81 0.65 0. 53 Bulk specific gravity after combust 0.600. 55 0. 50 0.65 Residuum after combustion. Soft Hard Very soft.

It is apparent that samples II and III are most desirable. If the fibercontent is equal to or exceeds 30%, as in sample IV, the bulk specificgravity of the composition increases after combustion, and the residuumis hardened into a pumice-like mass showing the poor heat retainingproperty.

The nature, utility, and detailed features of this invention areindicated more fully by the following examples of specific practiceconstituting preferred embodiments of the invention. It should beunderstood, of course, that these examples are presented as illustrativeonly, and that they are not intended to limit the scope of theinvention.

EXAMPLE 1 Four identical -ton flat molds were prepared each with its twolonger sides covered with heat-insulating lining frames and were chargedwith a desired material by pouring to initiate operation. Two slabs ofthe molds were supplied with 32 kg. each of a conventional exothermiccomposition, and the other two with 32 kg. each of an exothermiccomposition containing the following ingredients in the specifiedproportions in accordance with the present invention:

Powdered aluminum 15 Aluminum ash 50 Fluorspar 5 Sodium nitrate 3 Ironoxide 7 Asbestos (fiber length, about 2 mm.) 10

A considerable amount of fine particles was seen rising from the moldswhen supplied with the conventional composition, but almost none fromthe molds supplied with the fiber-containing composition of theinvention. During the succeeding process of combustion, the conventionalcomposition produced blowholes that sent the adjacent particles shootingup, obviously a sign of gas entrapment. Also during leveling operation,much particles and white colored smoke due to the exothermic reactionwere given off and densely suspended in the air.

No such phenomenon was caused by the exothermic composition of theinvention. Its residuum, too, was far softer and thicker layered thanthat of the sample of the prior art, evidencing its superiorheat-retaining property. In contrast to 86.3 and 86.2% yields indicatedby the use of the conventional composition, the fiber-containingcomposition of this invention with its improved heatretaining propertyled to the appreciably increased yields of 86.9 and 87.0%.

EXAMPLE '2 Two slabs of the four molds of Example 1 in operation weresimilarly supplied with 32 kg. each of a conventional exothermiccomposition, and the remaining two with 32 kg. each of compositioncontaining the following ingredients in accordance with the presentinvention:

Powdered aluminum 15 Aluminum ash 50 Fluorspar 5 Sodium nitrate 3 Ironoxide 7 Pulp (fiber length, about 5 mm.) 10

While a considerable amount of fine particles was seen rising from themolds when supplied with the conventional exothermic composition asstated already, almost no particles were set up from the molds suppliedwith this second example of the fiber-containing composition of theinvention. The phenomena previously seen with the molds supplied withthe conventional composition during combustion and leveling operationwere not caused by this second example either. Only the organic fiberswhen burning gave off red flames that rose barely to a height of about10 to 20 mm. The residuum of the charged composition was also far softerand thicker layered than that of the conventional composition and thusdemonstrated its superior heat retaining property. In comparison with86.0 and 86.2% yields indicated this time by the use of the conventionalcomposition, the fibercontaining composition of the invention made itpossible to secure yields of 86.8 and 86.9%.

EXAMPLE 3 Four identical ll-ton fiat molds were prepared each with itsall four sides covered with heat-insulating liningframes and were pouredwith a desired molten material for operation. Two slabs of the moldswere supplied with 30 kg. each of a conventional exothermic composition,and the other two with a composition containing the followingingredients in accordance with the present invention:

Powdered aluminum 15 Aluminum ash 55 Fluorspar 5 Sodium nitrate 3 Ironoxide 7 Amosite (fiber length, about 30 mm.) 5

While a considerable amount of fine particles was also seen rising fromthe molds when supplied with the conventional composition, substantiallyno such particles were blown upward from those supplied with the aboveprepared fiber-containing composition of the invention. Theaforedescribed phenomena during combustion and leveling operation werealso caused by the conventional composition but not by that of thepresent invention. As in the foregoing two examples, the residuum of thelatter was far softer and thicker layered than that of the former, hereagain indicating the superior heat-retaining property of the compositionof the invention. Compared with 82.6 and 83.2% yields obtained by theuse of the conventional composition, the use of the fiber-containingcomposition of the invention resulted in increased yields of 83.8 and84.0%.

We claim:

1. In a powdered exothermic hot top composition consisting essentiallyof a powdered flammable metal, an oxidizer, an oxidation accelerator,and an extender for particular use in retaining the heat of a hot top ona foundry mold by charging said composition onto the surface of the hottop and then causing said composition charged onto said surface to havecombustion, the "improvement comprising a fibrous material selected fromthe group consisting of a natural mineral fiber, an artificial mineralfiber, and a vegetable fiber each having a length of from about 0.5 mm.to about 30 mm. in an amount ranging from about 5% to about 30% byweight of said composition for forming in said composition numerouscavities, thereby retaining the heat of the hot top without trappinggases in said composition produced by said combustion and withoutreleasing the powder in said composition.

2. The composition as claimed in claim 1, in which said natural mineralfiber is asbestos.

3. The composition as claimed in claim 1, in which said artificialmineral fiber is selected from the group consisting of glass wool andslag wool.

4. The composition as claimed in claim 1, in which said vegetable fiberis selected from the group consisting of wood, pulp, paper, baggasse,and brans.

References Cited UNITED STATES PATENTS

